27'2 PHILOSOPHICAL TRANSACTIONS. [aNNO 1758: 



the practice could come up to the theory, they must certainly admit of very ex- 

 tensive ones, and of course bear very great magnifying powers. 



But the difficulties attending the practice are very considerable. In the first 

 place, the focal distances, as well as the particular surfaces, must be very nicelv 

 proportioned to the densities or refracting powers of the glasses; which are very 

 apt to vary in the same sort of glass made at different times. Secondly, the 

 centres of the two glasses must be placed truly on the common axis of the tele- 

 scope, otherwise the desired effect will be in a great measure destroyed. Add to 

 these, that there are 4 surfaces to be wrought perfectly spherical; and any per- 

 son, but moderately practised in optical operations, will allow, that there must 

 be the greatest accuracy throughout the whole work. 



Notwithstanding so many difficulties, as here enumerated, after numerous 

 trials, and a resolute perseverance, he brought the matter at last to such an issue, 

 that he could construct refracting telescopes, with such apertures and magnifying 

 powers, under limited lengths, as, in the opinion of the best and undeniable 

 judges, who have experienced them, far exceed any thing that has been hitherto 

 produced, as representing objects with great distinctness, and in their true 

 colours. 



XCIX. Of some Extraordinary Effects arising from Convulsions. By IV. 



fVatson, M. D,, F. R. S, p. 743. 



In January 1757, Dr. W. was concerned for a young gentlewoman, who, if 

 the number, continuance, and frequency of their returns, be considered, suffered 

 the most violent and severe convulsions he ever knew. At some times the mus- 

 cular spasms were general; at other times single muscles only, or a number of 

 them, subservient to some particular purpose in the animal economy, were af- 

 fected. And such was the peculiarity of this case, that after, and in proportion 

 as any single muscle, or any determined number of muscles, had been in a state 

 of spasm, a paralytic inability succeeded to those muscles, which very much dis- 

 ordered and impaired, and several times even for no small continuance prevented 

 the patient from performing several of her necessary functions. When the 

 muscles, for instance, subservient to deglutition had been convulsed, for many 

 hours after the fits had left her she had not been able to swallow a single drop of 

 liquid: so that when attempts had been made to cause her to drink, unless the 

 liquor was immediately thrown back, there was imminent danger of her being 

 strangled. When her eyes had been affected, several times a complete gutta 

 Serena, and total blindness, ensued; the patient being able to bear tlie strong 

 day-light with open eyes, without being sensible of its influence, or in the least 

 contracting her widely dilated pupils. After one of these fits the blindness con- 

 tinued full 5 days: and Dr. W. began to be in fear for the return of her sight. 



